1. Field of the Invention
The present invention relates to a semiconductor laser device protection circuit capable of protecting a semiconductor laser device from being broken by static electricity, and to an optical pickup apparatus and information recording/reproducing apparatus including the same. More particularly, the present invention relates to a semiconductor laser device protection circuit capable of protecting a semiconductor laser device that is used to record/reproduce information on a disk-shaped optical recording medium such as an optical disk or a magneto-optical disk from being broken by static electricity, and to an optical pickup apparatus and an information recording/reproducing apparatus which include the same.
2. Description of the Related Art
An optical pickup apparatus having a semiconductor laser device is used for an information recording/reproducing apparatus which records/reproduces information on an optical recording medium such as a compact disk (abbreviated as “CD”) or a digital versatile disk (abbreviated as “DVD”).
As a countermeasure against static electricity to protect the semiconductor laser device mounted in the optical pickup apparatus, the semiconductor laser device which is, for example, mounted on a substrate such as a flexible substrate or a hard substrate, has both terminals on the substrate directly connected to each other by soldering and thereby short-circuited. Owing to such a terminal-to-terminal short circuit of the semiconductor laser device, the semiconductor laser device can be protected from static electricity even when current generated by static electricity flows toward the semiconductor laser device. For achieving a short circuit between the both terminals of the semiconductor laser device, a technique has been developed that, for example, two short-circuiting patterns are formed in the optical pickup apparatus, and these two short-circuiting patterns are connected to the respective terminals of the semiconductor laser device while these two short-circuiting patterns are connected to each other by soldering.
In the above technique, it is necessary to perform a soldering work of the short-circuiting patterns in the stand-alone optical pickup apparatus, and to perform solder removal from the short-circuiting patterns upon incorporating the optical pickup apparatus into a recording/reproducing apparatus for optical recording medium. A problem may arise during the use of a soldering iron in the soldering work and solder removal because leak current may possibly flow through the semiconductor laser device due to a ground failure caused by the soldering iron.
In a semiconductor laser device protection circuit according to the technique disclosed by Japanese Unexamined Patent Publication JP-A 2006-49549, a semiconductor laser device is short-circuited by parallel connection of the semiconductor laser device with a chip resistor or a resistor made of an electrically-conductive material. The resistor connected in parallel to the semiconductor laser device protects the semiconductor laser device from static electricity. After completion of pickup adjustment, the connection with the chip resistor is cut in the case of using the chip resistor, or the electrically-conductive material is wiped or peeled off and thus removed in the case of using the electrically-conductive material, thereby bringing the semiconductor laser device out of the short-circuited state.
In the technique disclosed by JP-A 2006-49549, the resistor is used to protect the semiconductor laser device from the static electricity and therefore, the short-circuited state attributed to the resistor can be removed without using a soldering iron so that the flow of leak current can be avoided while there is another problem that after completion of pickup adjustment, a work is required for terminating the short-circuited state attributed to the resistor.
In the technique disclosed by Japanese Unexamined Utility Model Publication JP-U 6-52018 (1994), a laser diode protection circuit is connected to an anode of a laser diode in an optical information recording/reproducing apparatus. The laser diode protection circuit includes a transistor connected in parallel to the laser diode. Until a supply voltage being applied to the optical information recording/reproducing apparatus reaches such a supply voltage level that circuits other than the laser diode protection circuit normally operate, the transistor is energized to avoid current flow over the maximum rated value through the laser diode having its anode electrically grounded, so that the laser diode is prevented from breakage.
In the technique disclosed by JP-U 6-52018, although no current over the maximum rated value flows through the laser diode which can be thus prevented from breakage, there is a problem that electricity needs to be supplied also to the laser diode protection circuit and unless electricity is supplied to the optical pickup apparatus, the semiconductor laser device such as the laser diode cannot be protected.